Endless power transmission chains are frequently constructed of groups of transversely aligned links, referred to as sets or ranks of links. Each such link group is generally joined to and interleaved with the next adjacent set of links by transversely oriented pivot means, such as round pins or pin and rocker combinations, received in link openings provided adjacent the ends of each link. The openings in the sets of links are aligned with one another to receive the pivot means. Because of the interleaving of the links, there is one more link in each alternate set of links than in the two immediately adjacent sets of links. Some power transmission chains are used to drivingly interconnect the pulleys of a pulley transmission. When a chain is so used, it may be provided with drive or load blocks, each of which is positioned over the chain and between two adjacent pivot means. A chain-belt of this type is described and claimd in Cole et al, U.S. Pat. No. 4,313,730, issued Feb. 2, 1982. Another form of chain-belt to drivingly interconnect the pulleys of a pulley transmission is constructed so that the pivot means drivingly contact the pulley flanges. A chain-belt of this type is described in U.S. Pat. No. 4,344,761, issued Aug. 17, 1982.
One problem which arises when using a chain or a chain-belt for drivingly interconnecting the pulleys of a pulley transmission is the generation of noise which is disagreeable to humans. The noise caused by the impact of the chain-belt and pulleys is usually rhythmic and "bunched" in narrow frequency ranges; the noise can reach a level of about 80 dB. During impact of the chain-belt and the pulleys, the chain-belt acts in a manner similar to a rigid link chain when it impacts a sprocket because there is a radial as well as a longitudinal component of chain motion, and the radial link displacement is referred to as "chordal action." Chordal action occurs because the "pitch line" of an endless chain is polygonal, the pitch line being a series of joined straight lines, each extending between and joining the adjacent centers of articulation of the chain. The centers of articulation are those centers about which the chain pivots.
The drive or load blocks of a chain-belt as described in the Cole et al patent or the pivot members of a chain-belt as described in the aforesaid U.S. Pat. No. 4,344,761 impact the pulleys with generally the same action as that of a chain when it impacts a sprocket. Such chain-belt-pulley impact thus produces sound peaks in a regular pattern. Attempts have been made to break up the regular noise pattern, so that it is not objectionable to humans. Some attempts have been made to randomize the chain-belt impact with the pulleys, i.e., alter the previously regular time sequence of chain-belt-pulley impacts. Another suggested approach is to shorten the "pitch" of the links, where pitch is defined as the distance between points of articulation of the chain-belt. By shortening the pitch, the radial component of motion as the chain-belt engages the pulleys is reduced and the pitch line approaches a smooth, continuous line having curved portions. However, it is difficult to manufacture extremely short pitch chains which are suitable for the intended purpose, and pitches below 3/8 of an inch have been considered impractical from a manufacturing standpoint.